Method in a communication system

ABSTRACT

A method and arrangement are disclosed in a Vector Control Entity for enabling a fair bit rate distribution among lines of similar priority in a vectoring group, when applying partial vectoring in a DSL communication system. The method comprises calculating a rate balancing metric, RBM, for each line i within a priority group A, indicative of the ratio between the bit rate of a line i with a current vectoring resource allocation, and the estimated bit rate of line i assuming approximately no crosstalk within the vectoring group. The method further comprises allocating partial-vectoring resources to the line/s within the group A, based on the calculated RBMs, such as to reduce the difference in RBM between the lines. The method further comprises calculating an updated RBM for any line within the group A subjected to changes in vectoring resource allocation. The method may be iterated until certain criteria are fulfilled. The arrangement is adapted to enable the performance of the above described method.

TECHNICAL FIELD

The invention relates to a method and an arrangement in a DSL (DigitalSubscriber Line) system, in particular to cancellation of crosstalkusing partial vectoring.

BACKGROUND

Far-end crosstalk (FEXT) is a major problem significantly limiting theperformance of DSL systems. An ITU-T standard (TelecommunicationStandardization Sector of the International Telecommunication Union),G.993.5 [1], for cancelling FEXT by means of signal processing, has beendeveloped. This crosstalk cancellation technology is usually referred toas “vectoring” or “DSM (Dynamic Spectrum Management) level 3”technology.

Vectoring technology is assumed to be the core technology of the nextgeneration of DSL for cancelling the FEXT between DSL lines, and thusmaximize the DSL system performance. Vectoring technology will play avery important role in FTTx (Fiber To TheNode/Cabinet/Curb/Building/Home/Premises, etc.) business, because itenables offering 100 Mbps per user with DSL lines in the last hundredmeters, i.e. the distance between the end of a fiber network and theCPEs (Customer premises Equipments).

A schematic downstream vectoring arrangement is illustrated in FIG. 1.The downstream vectoring arrangement shown in FIG. 1 comprises aprecoder 102, for pre-cancelling of crosstalk. The precoder is locatedat the DSLAM (Digital Subscriber Line Access Multiplexer) side 106 of aDSL line bundle or cable 104. The cancellation of FEXT is done at theDSLAM side 106 of the DSL lines 110. Downstream FEXT is pre-cancelled byuse of a precoder 102 in the DSLAM, while upstream FEXT is cancelled byuse of an upstream crosstalk canceller in the DSLAM (not shown).According to an ITU-T recommendation, a way is provided to estimate theFEXT channel in both downstream and upstream, and to utilize theestimated channel to cancel the crosstalk

To explain the vectoring principle, referring to FIG. 1 and withoutconsidering the background noise, the received signals y₁, y₂, y₃ . . ., y_(n) at the different CPEs 1-N can be expressed in matrix form as:y=HPx  (1)where y=[y₁ y₂ . . . y_(N)]^(T) and y_(i) is the received signal at CPEi, x=[x₁ x₂ . . . x_(N)]^(T) and x_(i) is the transmitted signal of line1, H is the channel matrix, P is the precoding matrix doing crosstalkpre-cancellation, and X^(T) denotes the transpose of the vector X.

Applying a simple zero-Forcing technique and setting:P=H⁻¹  (2)results in:y=x  (3)Thus, the received signal equals the transmitted signal, and thus nocrosstalk is present in the received signal at the CPEs. Similarly, theupstream crosstalk can be cancelled by post-processing in an upstreamcrosstalk canceller at the DSLAM side.Partial Vectoring

The vectoring technology is a very attractive solution for VDSL2 [2]cabinet deployment, where vectoring enabled VDSL2 DSLAMs are installedin cabinets where hundreds of lines, typically, are connected to theusers. However, fully cancelling hundreds of lines is too costly interms of signal processing. Therefore, partial vectoring is consideredas a practical solution for vectoring by cancelling only a part of thecrosstalk/ers to each line, preferably the “strongest” crosstalk/ers.

FIG. 2 and FIG. 3 show a simplified partial-vectoring system model fordownstream and upstream, respectively. As shown in the system model, thepartial vectoring system illustrated in FIGS. 2 and 3 is capable ofcancelling a selected subset of the crosstalkers for each line. It hasbeen shown that close-to-optimal performance can be achieved by usingpartial vectoring. When using partial vectoring, weak crosstalk/ersis/are left unprocessed, and therefore, the use of partial vectoringenables a significant reduction of the computational complexity and costof vectoring systems.

However, there is a management issue to solve in partial vectoring,namely how to distribute the vectoring resources among the DSL lines,and how to determine which crosstalk/ers that should be cancelled oneach line. To manage the partial vectoring capability, ITU-T G.993.5 [1]defines two new configuration parameters related to partial vectoring:

-   -   Target Data Rates: referring to the expected data rates, for        downstream and upstream, respectively, which are achievable for        a line when all lines in the vectored group are active.    -   Line priorities (LOW/HIGH): partial vectoring should initially        allocate sufficient resources in such a way that the target data        rate is met for all the lines in the vectoring group. Then, the        remaining resources will be distributed to the lines with line        priority HIGH first to improve their data rates above the target        data rates until they reach the maximum data rates configured.        If the maximum data rate condition is met for all the vectored        lines with line priority HIGH, the remaining resources are        allocated to vectored lines with line priority LOW to improve        their data rates above the target data rate.

ITU-T G.993.5 [1] defines a vectoring initialization procedure, whichenables vectoring. This procedure is illustrated in FIG. 4. It should benoted that only the steps related to crosstalk cancellation are shown inFIG. 4, in order to simplify the discussion. Basically, ITU-T G.993.5defines a joining procedure in which the existing vectored lines, whichare already in showtime, are not interfered by the joining lines, whichinitialize to enter showtime, and eventually the mutual crosstalkbetween lines are cancelled after certain steps. This defined procedureis very straight forward to apply for full vectoring. However, whenapplying partial vectoring, it is not clear how to support therequirements of target data rates and line priorities duringinitialization.

Further, when regarding the crosstalk to a specific line, it is notclear how to allocate vectoring resources in order to achieve the bestpossible result from the allocated vectoring resources. A line i may besubjected to crosstalk from a number of different other lines in thesame vectoring group. The crosstalk from all the tones S of another linet to line i may vary over all the tones S of line i. Thus, it is amulti-dimensional problem to determine, and eventually cancel, thecrosstalk from each tone of each other line to each tone of line i. Ithas not even been defined how to determine which crosstalk that is the“strongest” crosstalk to a line. In addition, lines may have differenttarget rates and priorities, which should be regarded. All this takentogether imply that the task of allocating partial-vectoring resourcesamong lines and within lines is a problem which needs to be solved.

Since it is believed that partial vectoring is of great importance forfield deployment for computational complexity reasons, there is a needto have a vectoring resource allocation method, which supports partialvectoring, configured data rates and line priorities.

SUMMARY

It would be desirable to enable efficient allocation of vectoringresources to the lines in a partial vectoring DSL system, with regardtaken to target data rates and priorities of the lines. It is an objectof the invention to enable improved cancellation of crosstalk in apartial vectoring DSL system. Further, it is an object of the inventionto provide a method and an arrangement for vectoring resourcemanagement, which may be used e.g. in connection with initialization oflines when applying partial vectoring. These objects may be met by amethod and arrangement according to the attached independent claims.Embodiments are defined by the independent claims.

According to a first aspect, a method is provided in a Vector ControlEntity, for allocation of partial-vectoring resources in a DSLcommunication system. The method comprises calculating a rate balancingmetric, RBM, for each line i within a priority group A, indicative ofthe ratio between the bit rate of a line i with a current vectoringresource allocation, and the estimated bit rate of line i assumingapproximately no crosstalk within the vectoring group. The methodfurther comprises allocating partial-vectoring resources to the line/swithin the group A, based on the calculated RBMs, such as to reduce thedifference in RBM between the lines. The method further comprisescalculating an updated RBM for any line within the group A subjected tochanges in vectoring resource allocation.

According to a second aspect, an arrangement in a Vector Control Entityis provided. The arrangement is adapted to allocate partial-vectoringresources in a DSL communication system. The arrangement comprises afunctional unit, which is adapted to calculate a rate balancing metric,RBM, for each line i within a priority group A. The RBM is indicative ofthe ratio between the bit rate of line i with current vectoring resourceallocation, and the estimated bit rate of line i when assumingapproximately no crosstalk within the vectoring group. The functionalunit is further adapted to calculate an updated RBM for any line withinthe group A, which is subjected to changes in vectoring resourceallocation. The arrangement further comprises a functional unit, whichis adapted to allocate vectoring resources to the line/s within thegroup A, based on the calculated RBMs, when partial-vectoring resourcesare to be allocated among the lines within the vectoring group. Theresources should be allocated such as to reduce the differences in RBMbetween the lines.

The above method and arrangement may be used for enabling a fair ratedistribution among lines of similar priority when applying partialvectoring. The parameter RBM enables a comparison of the relative bitrates of the lines, and thus enabling allocation of resources to theline/s having the lowest relative bit rate.

The above method and arrangement may be implemented in differentembodiments. In some embodiments the allocation of partial-vectoringresources and a following update of RBM are repeated until one or morecriteria are fulfilled. The criteria may be fulfilled when the lowestRBM is equal to or larger than a predetermined threshold, or, when thereare not vectoring resources sufficient for cancelling the crosstalk fromanother line within the vectoring group to a line within the group A,left to allocate. Further, the criteria could be fulfilled when thereare not vectoring resources sufficient for cancelling any crosstalk leftto allocate. This feature enables ending of the allocation ofpartial-vectoring within a priority group when desired or needed. Theprocedure could e.g. continue in a group of lines having a lowerpriority than group A.

Further, in some embodiments, a line within group A is excluded fromallocation of vectoring resources, if the bit rate of said line wouldexceed a predetermined maximal bit rate after a further allocation ofvectoring resources. In some embodiments, a line within group A isexcluded from further allocation of vectoring resources if the crosstalkfrom the other lines within the vectoring group to said line isapproximately cancelled. This feature may ensure that the lines are notallocated more partial-vectoring resources than needed or desired.

In some embodiments, partial-vectoring resources are allocated to a linehaving a low RBM, as compared to the other lines within group A. Thiscould e.g. be the line having the lowest RBM within the group A. Thisfeature may ensure that partial-vectoring resources are allocated to thelines in a fair way, in terms of bit rate.

In some embodiments, partial-vectoring resources may be re-allocatedfrom one or more lines having a high RBM within a priority group, whenthere are insufficient available vectoring resources left to allocate toa line which is to be joined to the vectoring group, or to a line whichis to be upgraded to a higher priority. For example, partial-vectoringresources may be re-allocated from one or more lines having the highestRBM within a priority group. Thus partial-vectoring resources will bere-allocated from one or more lines having a high relative bit rate,i.e. a high RBM, as compared to other lines within the same prioritygroup, and thus reduce the differences in relative bit rate between thelines. This is enabled by use of the RBM.

The embodiments above have mainly been described in terms of a method.However, the description above is also intended to embrace embodimentsof the arrangement, adapted to enable the performance of the abovedescribed features. The different features of the exemplary embodimentsabove may be combined in different ways according to need, requirementsor preference.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail by means of exemplaryembodiments and with reference to the accompanying drawings, in which:

FIG. 1 is a schematic view illustrating a downstream vectoringarrangement, according to the prior art.

FIG. 2 is a block diagram illustrating a partial-vectoring system modelfor downstream, according to the prior art.

FIG. 3 is a block diagram illustrating a partial-vectoring system modelfor upstream, according to the prior art.

FIG. 4 is a flow chart illustrating initialization steps related tocrosstalk cancellation, according to the prior art.

FIG. 5 is a flow chart illustrating modified initialization stepsrelated to crosstalk cancellation.

FIG. 6 is a schematic view illustrating a priority group.

FIG. 7 is a flow chart illustrating procedure steps according to anembodiment.

FIGS. 8 and 9 are block diagrams illustrating arrangements, according toembodiments.

DETAILED DESCRIPTION

Briefly described, the invention enables balancing the rates among lineswithin the same priority group, such that each line achieves as equalpercentage of its single line performance as possible. This is achievedby determining which line/s that should be allocated partial-vectoringresources, based on a rate balancing metric (RBM).

Some Definitions

Within this document, some expressions will be used when discussing theprocedure of allocating vectoring resources, of which some will bebriefly defined here.

The term “vectoring group” is used as referring to the lines associatedwith the same precoder for the downstream vectoring and the samecanceller for the upstream vectoring.

The term “crosstalker” is used as referring to a line which subjectsanother line to crosstalk. When crosstalk to a line i is generated byand received from a line t, line t is a crosstalker of line i. One linemay have a plurality of crosstalkers and may also be a crosstalker to aplurality of lines. Expressions like “cancel a crosstalker”, and “cancelthe crosstalk/er”, are used in the meaning “cancel the crosstalk from acrosstalker to a line”.

The term “same” as in “lines having the same priority”, could also beinterpreted as, or expressed as, “approximately the same”, or “linesbelonging to the same priority group”.

A “joining line” is a previously inactive line, which is to be activatedand incorporated in a vectoring group. The line is thus a joining lineto the vectoring group.

Before describing the rate balancing metric and its use, another aspectof partial-vectoring resource allocation will be described.

Worst Crosstalk/er

Cognizant of the above described problems, it is realized that it wouldbe convenient to have a parameter indicating which crosstalk, i.e. thecrosstalk from which crosstalker, that is the “worst” crosstalk to aline, i.e. the crosstalk having the largest negative effect on the bitrate of the line subjected to crosstalk. Such a parameter should alsonot be too complex, in order to save computational resources and/ormemory storage capacity. However, it is not evident how such a parametershould be obtained.

Crosstalk Effect Indicator (CEI)

Within this disclosure, a parameter to address at least some of theabove mentioned problems is suggested, in the form of a Crosstalk EffectIndicator (CEI). A value of the CEI parameter can be determined, whichindicates to which extent the rate of a line is affected by thecrosstalk from a certain crosstalker. The CEI could also be denoted e.g.“capacity loss indicator”, “rate improvement indicator” or “crosstalkstrength indicator”. A high CEI-value indicates that the bit rate of theline in question is highly reduced due to the crosstalk in question,i.e. also indicating that the bit rate of the line could be highlyincreased if said crosstalk was to be cancelled. Accordingly, a low CEIvalue indicates that the line in question is not very affected by thecrosstalk in question, and that the bit rate of the line would not beparticularly increased by cancelling said crosstalk. Each CEI-value is anumber, associated with the crosstalk from one crosstalker to one line.Thus a CEI-value consumes little memory to record and is easy to use forranking or sorting crosstalk/ers according to effect on the bit rate ofthe line subjected to the crosstalk. The CEI will be described infurther detail below.

Computation of CEIs

Below, it will be described how CEIs can be calculated for the crosstalkfrom each crosstalker of interest, to a line.

Channel Estimation

According to ITU-T G.993.5 [1], the normalized crosstalk channelcoefficients can easily be estimated from error sample feedback fromCPEs in downstream and from the received signal, or error samples, atthe DSLAM in upstream. At tone k, the normalized crosstalk channelcoefficients from line j to line i can be expressed as

$\begin{matrix}{{\overset{\_}{h}}_{ij}^{k} = \frac{h_{ij}^{k}}{h_{ii}^{k}}} & (4)\end{matrix}$where h_(ij) ^(k) is the crosstalk channel coefficient from line j toline i at tone k, and h_(ij) ^(k) is the direct channel of line i attone k. Here, the channel estimation algorithm is not given, since it issomewhat outside the scope of this solution.Interference-to-Signal Ratio

Utilizing the channel estimation results, the interference-to-signalratio from line j to line i at tone k can be expressed as:

$\begin{matrix}{{I\; S\; R_{ij}^{k}} = {\frac{P\; S\; D_{j}^{k}}{P\; S\; D_{i}^{k}} \cdot {{\overset{\_}{h}}_{ij}^{k}}^{2}}} & (5)\end{matrix}$where PSD_(t) ^(k) is the transmit PSD of line t at tone k, |X| denotesthe absolute value of X, and h _(ij) ^(k) the normalized crosstalkchannel coefficients from line j to line i at tone k, which can beestimated From the error sample feedback from CPEs in downstream and thereceived signal, or error samples, at DSLAM in upstream.CEI Definition

For a line i, the CEI is defined as:

$\begin{matrix}{{cei}_{ij} = {\sum\limits_{k \in S_{tone}}{\log\; I\; S\; R_{ij}^{k}}}} & (6)\end{matrix}$where log(X) denotes the natural logarithm of X, ISR_(ij) ^(k) theinterference-to-signal ratio from line j to line i at tone k, andS_(tone) is a subset of tones which are taken into account. The S_(tone)could comprise all downstream or upstream tones of a line, but forcomputational complexity reasons, a subset of tones is preferable.

The CEI is thus an indicator of the impact or effect of the crosstalkfrom one line to another on the capacity or bit rate of the linesubjected to the crosstalk. The definition of CEI reflects the capacityof a line i when being subjected to crosstalk from only one line, j. Inthe CEI, the tone-wise crosstalk strength variation is smoothed withrespect to capacity. Further, it can be proved that cancelling thecrosstalker associated with the largest CEI will give the largestcapacity/bit rate improvement when canceling one of the crosstalkers.Thus, a CEI-value is suitable for determining how the bit rate of a lineis affected by the crosstalk from a certain crosstalker. For example, aline 2 is considered as a stronger crosstalker to a line 1 than a line 3when cei₁₂>cei₁₃. The complexity of the CEI calculation can besignificantly reduced by reducing the number of tones in the pluralityor set S_(tone). As each CEI is just a single number for onecrosstalk/er to one line, it consumes little memory to record and it isalso easy to be used to sort or rank crosstalk/ers. Henceforth, the term“strongest”, e.g. in the context “the strongest crosstalk/er”, is usedas referring to the crosstalk/er associated with the highest CEI, of aline.

New Line Control Parameters

In an exemplary embodiment, the following line control parameters aredefined in addition to the CEI discussed above, to be used when managingpartial vectoring initialization:

-   -   Crosstalk effect indicator list (CEIL);    -   Sorted crosstalker list (SXL);    -   Number of crosstalkers to be cancelled: M;    -   Out-of-domain noise-to-signal ratio vector (ODNSRV);        Even though the CEIL and the SXL here are described in terms of        lists, there may also be embodiments of the invention which do        not use an actual list, but instead keep track or record of the        CEIs and the relation between different CEIs in some other way,        e.g by associating a ranking value to each CEI of a line, and/or        by parsing of CEI values in an unsorted list, record, or        similar. The parameters could be named differently, if        preferred.

For a line i, the above parameters are defined as follows:

-   -   The crosstalk effect indicator list (CEIL) is defined as:        ceil_(i)={cei_(i1), . . . ,cei_(i(i−1)),cei_(i(i+1)), . . .        ,cei_(i(N−1))}  (7)        where cei_(ij) is the crosstalk effect indicator (CEI) of the        crosstalk from line j to line i, and N is the number of lines in        the vectoring group. There are two Crosstalk effect indicator        lists, ceil_(i) ^(d) and ceil_(i) ^(u), for downstream (d) and        upstream (u), respectively, as downstream and upstream use        different tone sets, i.e. S^(d) _(tone)≠S^(u) _(tone).

The sorted crosstalker list (SXL) is defined as:sxl_(i)={j_(i1),j_(i2), . . . ,j_(i(N−1))}  (8)where j_(it) is the crosstalker index of the tth crosstalker in the SXLof line i, and N is the number of lines in the vectoring group. TheSXL-parameter sorts the crosstalkers of each line in the order of theCEI of the crosstalk from the crosstalkers.There are two sorted crosstalker lists, sxl_(i) ^(d) and sxl_(i) ^(u),for downstream (d) and upstream (u), respectively, as downstream andupstream use different tone sets.

The number of crosstalkers from which the crosstalk to line i is to becancelled is defined as: M_(i), where M_(i) is the number of thestrongest or worst crosstalk/ers, i.e. the crosstalk/ers having thehighest CEIs, which are to be cancelled on line i in order for line i toachieve its target rate. Therefore, the crosstalk/ers to be cancelledare the first M_(i) crosstalkers in sxl_(i). M_(i) is determined usingthe rate estimation algorithm, which will be described further below.

There are two numbers of crosstalkers to be cancelled, M_(t) ^(d) andM_(i) ^(u), for downstream and upstream, respectively, as downstream andupstream use different tone sets and have different target rates.

The out-of-domain noise-to-signal ratio vector (ODNSRV) is defined as:odnsrv_(i)={odnsr_(i) ⁰,odnsr_(i) ¹, . . . ,odnsr_(i) ^(N) ^(C) ⁻¹}  (9)where odnsr_(t) ^(k) is the out-of-domain noise-to-signal ratio (ODNSR)of line i on tone k, and N_(c) is the number of tones per. Theout-of-domain noise (ODN) is the noise from outside of the vectoringgroup, such as alien crosstalk from legacy DSL systems in the samebinder/cable, the background noise at the DSL receiver and other noisefrom outside of the vectoring system. The ODNSR is the noise-to-signalratio when there is basically no crosstalk between the lines in the samevectoring group.Obtaining the ODNSR

The ODNSR can be obtained in different ways. For joining lines, i.e.lines which are initialized into a vectoring group, the ODNSR can becalculated as:

$\begin{matrix}{{odnsr}_{i}^{k} = \frac{O\; D\; N_{i}^{k}}{P\; S\;{D_{i}^{k} \cdot {Attn}_{i}^{k}}}} & (10)\end{matrix}$where ODN_(i) ^(k) is the out-of-domain noise power of line i at tone k,PSD_(i) ^(k) is the transmit PSD of line i at tone k, and Attn_(i)^(k)=|h_(ii)|² is the line attenuation of line i at tone k.

In this disclosure, the electrical length is used to estimate the lineattenuation as

$\begin{matrix}{{Attn}_{i}^{k} = 10^{\frac{l_{i}\sqrt{k \cdot f_{t}}}{10}}} & (11)\end{matrix}$where l_(i) is the electrical length of line i and f_(t) is the tonespacing in MHz. The benefit of using the electrical length is that theelectrical length is available before the decision process of whichcrosstalkers that are to be cancelled.

In addition, ODN_(i) ^(k) can be assumed or estimated based on labmeasurements and/or theoretical models. The assumed value of ODN_(i)^(k) should be selected conservatively to be an upper bound of the trueout-of-domain noise level such that the out-of-domain noise is notunderestimated.

For lines in showtime, the showtime signal-to-noise ratio (SNR) can bemeasured. Thus, for lines in showtime, which are already vectored, theODNSR can be calculated as

$\begin{matrix}{{odnsr}_{i}^{k} = {\frac{1}{S\; N\; R_{i}^{k}} - {\sum\limits_{j \notin C_{i}}{I\; S\; R_{ij}^{k}}}}} & (12)\end{matrix}$where SNR_(i) ^(k) is the measured showtime signal-to-noise ratio attone k, C_(i) is the set of crosstalkers which are cancelled by thedownstream precoder or upstream crosstalk canceller, and ISR_(ij) ^(k)is the interference-to-signal ratio from line j to line i at tone k.Actually,

$\sum\limits_{j \notin C_{i}}{I\; S\; R_{ij}^{k}}$is the interference-to-signal ratio between the joining lines to theline i.

It is further realized that SNR term in (12) for a line, in fact, couldbe derived/estimated from the Quiet Line Noise (QLN) measurement, whichis performed during initialization. For upstream, the QLN results can beobtained from the DSLAM receivers. For downstream, this would requirethat the QLN results are provided to the VCE/DSLAM side from the CPEside, where the downstream QLN measurement is performed. When QLNresults are available, the SNR term in (12) for line i at tone k can beestimated as:

$\begin{matrix}{{S\; N\; R_{i}^{k}} = \frac{P\; S\;{D_{i}^{k} \cdot {Attn}_{i}^{k}}}{Q\; L\; N_{i}^{k}}} & (13)\end{matrix}$where PSD_(i) ^(k) is the transmit PSD of line i at tone k, and Attn_(i)^(k)=|h_(ii)|² is the line attenuation of line i at tone k. And Attn_(i)^(k) can be calculated using (11) with the electrical length. Therefore,when QLN results are available in initialization, the ODNSR should becalculated using (12) with (13), instead of using (10).

The ODNSR calculated using (12), based on a showtime SNR can be used inshowtime to fine-tune the vectoring parameters and the cancellationcoefficients because the showtime SNR is more accurate. This will befurther described below.

Rate Estimation Algorithm

The raw bit rate of each line may then be estimated as:

$\begin{matrix}{{\overset{\sim}{R}}_{i} = {f_{s} \cdot {\sum\limits_{k}{\min\left( {{{round}\left( {\log_{2}\left( {1 + \frac{1}{\left( {{\sum\limits_{j \notin C_{i}}{I\; S\; R_{ij}^{k}}} + {odnsr}_{i}^{k}} \right) \cdot \Gamma}} \right)} \right)},15} \right)}}}} & (14)\end{matrix}$where f_(s) is symbol rate in Hz, min(X,Y) takes the minimal value of Xand Y, round(X) rounds X to the nearest integer, Γ is the SNR gap, C_(i)is the set of crosstalkers which are assumed to be cancelled, ISR_(ij)^(k) the interference-to-signal ratio from line j to line i at tone k,odnsr_(i) ^(k) is the out-of-domain noise-to-signal ratio of line i attone k, and the number 15 is the maximum number of bits that can be usedto modulate a tone.

The actual bit rate considering other overheads, i.e. coding overheadand sync symbol overhead, can be estimated as:

$\begin{matrix}{{\hat{R}}_{i} = {\left( {{\overset{\sim}{R}}_{i} - \frac{N_{b} \cdot f_{s}}{2}} \right) \cdot \frac{256}{257} \cdot \left( {1 - \frac{{2 \cdot I}\; N\; P_{\min}}{{Delay}_{\max} \cdot f_{s}}} \right)}} & (15)\end{matrix}$where N_(b) is the number of tones/subcarriers with at least 1 bitloaded, INP_(min) is the minimum impulse noise protection (INP)configured in DMT symbols, Delay_(max) is the maximum allowed delay inseconds and f_(s) is symbol rate in Hz.

Both downstream and upstream bit rates, R_(i) ^(d) and R_(i) ^(u), canbe estimated using (14) with the corresponding downstream and upstreamtone set, respectively.

Modified Initialization Procedure

An exemplary modified initialization procedure for partial vectoring isshown in FIG. 5. The illustrated procedure is involved with updating thenew defined line control parameters and cancelling the crosstalkersaccordingly. In FIG. 5, the steps comprising bold text illustrate themodified steps. The illustrated procedure can be used to ensure that theshowtime bit rate of each line will be approximately the target rate,and not much higher. If the rate estimation works successfully, theshowtime bit rate of each line should be equal to, or at leastrelatively close to, its target rate.

The modified procedure illustrated in FIG. 5 could be described asfollows, concentrating on the modified actions. Initially, in an action502, the downstream parameters ceil_(i) ^(d), sxl_(i) ^(d) and M_(i)^(d) of each existing vectored line i are updated, based on downstreamerror samples. Then, the coefficients of the precoder are calculated andupdated to pre-cancel, only, the first M_(i) ^(d) crosstalkers insxl_(i) ^(d) for each existing vectored line i. Here, all SXLs areassumed to be sorted in a descending order, i.e. having the highestCEI-value first.

Further, in an action 504, the upstream parameters ceil_(i) ^(u),sxl_(i) ^(u) and M_(i) ^(u) of each existing vectored line i areupdated, based on received upstream sync symbols or error samples. Then,the coefficients of the upstream canceller are calculated and updated tocompletely cancel, only, the first M_(i) ^(u) crosstalkers in sxl_(i)^(u) for each existing vectored line i.

In a next action 506, the downstream parameters ceil_(i) ^(d), sxl_(i)^(d) and M_(i) ^(d) of each joining line i, are updated based ondownstream error samples of the joining lines. Then, the downstreamprecoder coefficients are calculated and updated to pre-cancel, only,the first M_(i) ^(d) crosstalkers in sxl_(i) ^(d) for each joining linei.

Further, in upstream, the parameters ceil_(i) ^(u), sxl_(i) ^(u) andM_(i) ^(u) each joining line i are updated based on received upstreamsync symbols or error samples. Then, the coefficients of the upstreamcanceller are calculated and updated to cancel, only, the first M_(i)^(u) crosstalkers in sxl_(i) ^(u) for each joining line i.

Then, in a next step 508, the target data rate of each joining line isconfigured as the maximum data rate. Then the joining lines proceed withthe rest of VDSL2 initialization and get into showtime. Theconfiguration here is optional to avoid over-allocation of the partialvectoring resources to each line, when the rate of each line is notallowed to change in showtime. However, this configuration is not neededwhen any rate adaptation technique (e.g. Seamless Rate Adaptation) issupported in showtime.

Fine-Tune Parameters and Update Coefficients in Showtime

During initialization of a line or a DSLAM, when QLN results are notavailable, the ODNSR may be estimated using (10). In (10), theout-of-domain noise power spectrum density is conservatively assumedbased e.g. on offline measurement like lab measurement and/ortheoretical models, or based on QLN measurements. Therefore, a rateestimation using (14) and (15) based on (10) is likely to underestimatethe bit rate and thus over-cancel the number of crosstalkers. Even whenQLN results are available, the ODNSR estimation in initialization by(12) and (13) is not as accurate as using (12) with the showtime SNRmeasurement. When joining lines have entered showtime, the showtime SNRmay be measured, and thus the ODNSR may be re-estimated from themeasured showtime SNR by use of (12) to improve the rate estimation.Accordingly, the number of crosstalkers to be cancelled, M_(i) ^(d) andM_(i) ^(u), in downstream (d) and upstream (u), respectively, may bere-determined. Finally, the precoder and uplink canceller coefficientscould be updated to cancel only the first M_(i) ^(d) and M_(i) ^(u)crosstalkers in sxl_(i) ^(d) and sxl_(i) ^(u) for downstream andupstream, respectively

Distribution of Remaining Vectoring Resource Among e.g. High PriorityLines

After initialization, or otherwise, when all lines have been assignedpartial-vectoring resources sufficient for reaching their target bitrate, there may still be vectoring resources left. These remainingresources could be distributed among the lines, such that the linesattain a bit rate, which is higher than the target bit rate, andpossibly as high as the maximum bit rate configured or the maximumachievable bit rate without crosstalk within the vectoring group if themaximum bit rate is set to unbounded.

One way of handling the allocation of remaining resources could be todivide the remaining vectoring resources equally between high prioritylines. However, such equal division would favor the short DSL lines,which are not as much subjected to crosstalk as longer lines. Thus, theshort lines would most probably attain relatively higher bit rateimprovements than the longer lines, when being allocated the same amountof vectoring resources, which may be considered unfair.

Nevertheless, after achieving the target rate of each line in avectoring group, any remaining vectoring resources could be dividedbetween the lines, e.g. following certain predetermined criteria orrules, e.g. until these lines attain their maximum bit rate. One of thesimplest rules would then be to equally divide the remaining resourcesbetween the high priority lines, as mentioned above. If there were to beany vectoring resources left when the high priority lines have attainedtheir maximum bit rate, the remaining vectoring resources could bedistributed among the low priority lines, in accordance with the linepriority definition in ITU-T G.993.5 [1].

The distribution of remaining or other vectoring resources could also bemade on request from the management system, before all lines to bejoined in the same vectoring group are joined. This could be useful whenthe lines are not fully used to provide service.

Cognizant e.g. of the fairness problem of distribution of remainingpartial-vectoring resources, it is realized that it would be convenientto have a parameter indicating which line that is in largest need ofvectoring resource allocation, in terms of achieved bit rate. Then afair distribution balancing the need for vectoring resource among thelines in the same priority group could be achieved by balancing theparameter. However, the line conditions, such as e.g. loop attenuationand out-of-domain-noise level, are different from line to line.

It is realized that the achieved percentage of the maximum achievablebit rate without crosstalk within the vectoring group would be a fairparameter to compare between the lines. This parameter indicates howmuch potential bit rate that is left to be achieved by cancelling morecrosstalkers. Balancing the percentage would enable each line in thesame priority group to achieve more or less the same percentage of itsmaximum achievable rate. Thus, each line will enjoy the vectoring gainfairly A simplified illustration of a vectoring group 602 and a prioritygroup 604 is shown in FIG. 6. However, it should be noted that the lineswithin a priority group do not need to be located together, asillustrated in FIG. 6, but could be scattered within a vectoring groupor bundle 602. It should be noted that a fair distribution ofpartial-vectoring resources may not be the most optimal distribution interms of total bit rate of a group of lines.

Rate Balancing Metric, RBM

Having knowledge of the parameters previously defined in thisdisclosure, e.g. the Crosstalk Effect Indicator, CEI, it is realizedthat a parameter in the form of a rate balancing metric, RBM, indicatingwhich line that is in largest need of further vectoring resources, couldbe attained as follows:

For a line i, the RBM when the M_(i) strongest crosstalkers of line iare cancelled, may be defined as:

$\begin{matrix}{{R\; B\;{M_{i}\left( M_{i} \right)}} = \frac{R_{i}\left( M_{i} \right)}{{\overset{\_}{R}}_{i}}} & (16)\end{matrix}$where R_(i)(M_(i)) is the bit rate of line i when the M, strongestcrosstalkers are cancelled, and R _(i) is the maximum achievable bitrate on line i without crosstalk within the vectoring group, i.e. whenonly ODN is present.The RBM can be estimated as

$\begin{matrix}{{R\; B\;{M_{i}\left( M_{i} \right)}} = \frac{\sum\limits_{k}{\log_{2}\left( {1 + \frac{{SIN}\;{R_{i}^{k}\left( M_{i} \right)}}{\Gamma}} \right)}}{\sum\limits_{k}{\log_{2}\left( {1 + \frac{S\; O\; D\; N\; R_{i}^{k}}{\Gamma}} \right)}}} & (17)\end{matrix}$where SINR_(i) ^(k)(M_(i)) is the signal-to-interference-and-noise ratioof line i at tone k assuming that the M_(i) strongest crosstalkers ofline i are cancelled, SODNR_(i) ^(k) is thesignal-to-out-of-domain-noise ratio of line i at tone k, and Γ is theSNR gap.

The estimation of SINR_(i) ^(k)(M_(i)) and SODNR_(i) ^(k) can be donewith crosstalk channel estimation and measured SNR, which can be easilyobtained from the vectoring initialization and showtime measurement,respectively.

The complexity of (17) can be reduced with the selection of a subset ofthe tones. Using a subset of the tones of line i is a goodapproximation, as the vectoring gains, e.g. from cancelling acrosstalker, are similar in all tones of a line.

There will be two RBMs for a line, RBM_(i) ^(d) and RBM_(i) ^(u), fordownstream (d) and upstream (u), respectively, as the noise environmentcould be different in downstream and upstream.

As previously described, the sorted crosstalker list (SXL) of line i isdefined as:sxl_(i)={j_(i1),j_(i2), . . . ,j_(i(N−1))}  (18)where j_(it) is the crosstalker index of the tth crosstalker in the SXLof line i. The SXL is a list, where the crosstalkers of a line aresorted according to strength of crosstalk to said line. The crosstalkerof j_(it) is deemed as a stronger crosstalker than the crosstalker ofj_(it+1), where t=1, . . . , N−1. Cancelling the M_(i) strongestcrosstalkers of line i corresponds to cancelling the first M_(i)crosstalkers in sxl_(i).Number of Crosstalkers to Cancel

When defining the total number of crosstalkers, which the vectoringsystem can cancel given, e.g., a certain processing capacity, as M_(T),the remaining vectoring resource could be expressed as:

$\begin{matrix}{M_{R} = {M_{T} - {\sum\limits_{i = 1}^{N}M_{i}}}} & (19)\end{matrix}$where N is the number of lines subjected to vectoring in the vectoringgroup. After further resource allocation, the number of crosstalkers tobe cancelled on line i is{tilde over (M)} _(i) =M _(i) +M _(i)′  (20)where M_(i) is the number of crosstalkers cancelled to achieve thetarget bit rate and M_(i)′ is the number of crosstalkers to be cancelledusing allocated remaining vectoring resources.

There are two numbers {tilde over (M)}_(i), of crosstalkers to becancelled, {tilde over (M)}_(i) ^(d) and {tilde over (M)}_(i) ^(u), fordownstream and upstream, respectively, as both M_(i) and M_(i)′ may bedifferent for downstream and upstream.

After the remaining vectoring resources have been allocated, thedownstream precoder coefficients may be calculated and updated topre-cancel e.g. the first {tilde over (M)}_(i) ^(d) crosstalkers insxl_(i) ^(d) for line i in downstream, and the upstream crosstalkcanceller coefficients may be calculated and updated to cancel the first{tilde over (M)}_(i) ^(u) crosstalkers in sxl_(i) ^(u) for line i inupstream. Then, the improved bit rates can be achieved by seamless rateadaptation (SRA) or retrain.

Re-Allocation of Resources

Vectoring resources may be reserved, e.g. for the event that a line isto join the vectoring group. However, when there are no, or insufficientpartial-vectoring resources reserved when a line is to join, e.g. agroup of lines having the same priority, or be upgraded to a higherpriority and thus be added to a new priority group, the vectoringresources required for such joining or upgrading could be re-allocatedfrom other lines within the vectoring group. Such re-allocation could bebased on calculated RBM-values in an “inverse” manner, as compared tohow the RBM-values are used when allocating vectoring resources tolines. The required vectoring resources, or part thereof, could betaken, or re-allocated, from one or more lines having a high RBM ascompared to other lines e.g. in the same priority group.

Typically, vectoring resources should be re-allocated from the line/shaving the highest RBM within a priority group, and thus having achievedthe highest percentage of their maximum achievable bit rate. When thereare lines of a lower priority than the joining or upgrading line/s,which have a bit rate exceeding their target bit rate, vectoringresources could be re-allocated from these lines of lower priority.Alternatively, or as well, vectoring resources could be re-allocatedfrom the lines having the highest RBM-values within the same prioritygroup as the joining or upgrading line/s. The above described “inverse”RBM re-allocation strategy will result in a fair re-allocation ofpartial-vectoring resources, in terms of relative bit rate.

Iterative Rate Balancing Algorithm

Below, an iterative rate balancing algorithm according to one embodimentwill be described. The algorithm can be used to balance the bit rates inboth downstream and upstream. To simplify the description, a generalalgorithm is given below with some general parameters without mentioningdownstream or upstream. In practice, the general parameters should bereplaced with the corresponding downstream or upstream parameters.

Algorithm Parameters

The following parameters are defined for the algorithm:

-   -   1. The total number of lines in the vectoring system: N.    -   2. The total number of crosstalkers which the vectoring system        can cancel: M.    -   3. Number of crosstalkers to be cancelled: M_(i)        -   M_(i) is the number of the strongest crosstalkers which are            to be cancelled on line i. Therefore, the crosstalkers to be            cancelled on line i is the first M_(i) crosstalkers in            sxl_(i).    -   4. The number of remaining crosstalkers the vectoring system can        cancel:

$M_{R} = {M - {\sum\limits_{i}M_{i}}}$

-   -    where iε{1, 2, . . . , N−1}.    -   5. List of lines to be balanced: L={l₁, l₂, . . . } where l_(t)        is the tth line index in L.    -   6. The estimated bit rate of line i when the M_(i) strongest        crosstalkers of line i are cancelled: R_(i)(M_(i)).    -   7. Maximum bit rate: R_(MAX,i).    -   8. Rate balancing metric: RBM_(i).        Rate Balancing Algorithm        The algorithm below will balance the RBM of each line. It works        iteratively, such that each iteration adds one more crosstalker        to be cancelled for the line which has the lowest RBM until all        the crosstalkers of said line are to be cancelled. The algorithm        ends when all vectoring resources are allocated to the lines or        all lines have reached their maximum bit rates.

Step 1: Load current M_(i) of each line in L. If there is no M_(i)available, then M_(i) = 0. Step 2: Calculate RBM_(i)(M_(i)) where i ε L.Step 3:${{Calculate}\mspace{14mu} M_{R}} = {{M - {\underset{i}{\Sigma}\mspace{14mu} M_{i}\mspace{14mu}{where}\mspace{14mu} i}} \in \left\{ {1,2,\ldots,{N - 1}} \right\}}$Step 4: If M_(R) = 0 or L is empty Algorithm ends else Continue to step5 end Step 5:${{Find}\mspace{14mu}\nu} = {\underset{i \in L}{\arg\mspace{14mu}\min}\left( {RBM}_{i} \right)\mspace{14mu}{and}\mspace{14mu}{estimate}\mspace{14mu}{R_{\nu}\left( M_{\nu} \right)}}$Step 6: If M_(ν) < N − 1 and R_(ν)(M_(ν)) < R_(MAX,ν) M_(ν) = M_(ν) + 1Update RBM_(ν)(M_(ν)) M_(R) = M_(R) − 1 Go to step 4 else Remove ν fromL Go to step 5 endExample Procedure, FIG. 7

An exemplary procedure for allocation of vectoring resources to lines ofthe same priority in a vectoring group, when applying partial vectoring,could be described as follows, with reference to FIG. 7. Initially, itis determined, in an action 702, whether vectoring resources should beallocated. The vectoring resources to be allocated could be e.g. theremaining resources after initialization of a number of lines.Alternatively, there are no remaining resources, but a need forresources to be re-allocated, e.g. to a line, which is to join thevectoring group.

When vectoring resources are to be allocated, RBMs are calculated forthe respective lines in a group A of lines having the same priority, inan action 704. Each line will thus have an RBM, indicating how close theline is to attaining its maximum rate. More precisely, the RBM isindicative of the ratio between the bit rate of a line i with a currentvectoring resource allocation, and the estimated bit rate of line i whenassuming approximately no crosstalk within the vectoring group. In anext action 706, it may be determined whether any or all the lines inthe group A have already attained the maximum rate, in which cases theprocedure could remove the lines having attained their maximum bit ratefrom further allocation, or end the procedure, respectively.

In a next action 708, it is determined which of the lines in the group Athat should be assigned vectoring resources, based on the calculatedRBMs. Typically, this would be the line having the lowest RBM. The linehaving the lowest RBM is the line having the lowest relative bit rateamong the lines in the group A, i.e. the line reaching the lowestpercentage of its maximum rate. Then, vectoring resources are allocatedto the determined line. The amount of resources allocated to the lineshould typically be sufficient for cancelling at least the crosstalkfrom the “worst” crosstalker, i.e. the crosstalk having the largesteffect on the bit rate of the line.

After resources have been allocated to a line in action 708, the RBM forsaid line is updated in an action 710. Then, it may be evaluated, e.g.in action 706, whether there still are vectoring resources that shouldbe allocated, and whether the lines have reached their maximum bit ratesor a predetermined percentage thereof. When there are still vectoringresources to be allocated and the lines in group A have not yet reachede.g. their maximum bit rates, the procedure may return to action 708,where it is determined which next line that should be assigned vectoringresources. It could be the same line, but it could also be another line,which after the last allocation and RBM update has e.g. the lowest RBM.

Thus, the procedure may continue to allocate vectoring resources in aniterative manner until all lines in group A have attained e.g. theirmaximum bit rate or until there are no further resources to allocate. Incase of re-allocation, the procedure may end when no further vectoringresources need to be re-allocated. Further, the process may end when thelowest RBM is equal to or exceeds a predetermined threshold, which doesnot necessarily need to correspond to that the lines have attained theirmaximum bit rate, but could correspond e.g. to a certain percentage ofthe maximum bit rate.

When the desired bit rates are attained in group A, or when there are nomore vectoring resources to allocate, the crosstalkers associated withthe highest CEIs may be cancelled for each line, using the vectoringresources allocated to the respective lines during the precedingprocedure. Possible remaining vectoring resources may then be allocatedwithin another group of lines having a lower priority than group A in asimilar way as described above.

Further, when there are no, or insufficient partial-vectoring resourcesreserved for the event that a line is to join group A or be upgraded togroup A, the vectoring resources required for such joining or upgradingcould be re-allocated from other lines within the vectoring group.

Example Embodiment, FIG. 8

Below, an exemplary arrangement 800 in a VCE 801, adapted to enable theperformance of the above described procedure, will be described withreference to FIG. 8.

The arrangement 800 comprises a determining unit 802, which is adaptedto determine whether there are vectoring resources to be allocated amonga group of lines having the same priority, or whether certain otherpredetermined criteria, e.g. concerning the lines, are fulfilled. Forexample, one such criterion could be fulfilled when a line has achieveda certain predetermined percentage of its maximum bit rate, and anothercriterion could be fulfilled when all lines in the group of lines havingthe same priority have achieved a certain predetermined percentage oftheir maximum bit rate, i.e. the lowest RBM is equal to or larger than apredetermined threshold.

The arrangement 800 further comprises a calculating unit 804, which isadapted to calculate a respective RBM for each line in a group A oflines having the same priority. The calculating unit 804 is furtheradapted to calculate an updated RBM for any line within the group A,which is subjected to changes in vectoring resource allocation.

The arrangement 800 further comprises an allocating unit 806, which isadapted to allocate partial-vectoring resources to the line/s within thegroup A, based on the calculated RBMs. In other words, the allocatingunit 808 is adapted to determine which line/s that should be assignedpartial-vectoring resources, based on the respective RBM of the lines.The partial-vectoring resources should be allocated such as to reducethe differences in RBM between the lines. Typically, this would implyallocating resources to the line having the lowest RBM. The allocatedvectoring resources should, typically, be used to cancel the crosstalkhaving the largest negative impact on the bit rate of the determinedline. The action of providing the results from the allocation unit 806to e.g. a precoder is illustrated as a dashed arrow from the determiningunit 802, controlling an equally dashed switch on the arrow fromallocation unit 806.

Further, the allocation unit 808 may be adapted to re-allocatepartial-vectoring resources from one or more lines within the vectoringgroup to a line joining group A or being upgraded to group A. Suchre-allocation may be required when there are no, or insufficient,partial-vectoring resources reserved for the event that a line is tojoin group A or be upgraded to group A.

Example Embodiment, FIG. 9

FIG. 9 schematically shows an embodiment of an arrangement 900 in aVectoring Control Entity, which also can be an alternative way ofdisclosing an embodiment of the arrangement in a Vectoring ControlEntity illustrated in FIG. 8. Comprised in the arrangement 900 are herea processing unit 906, e.g. with a DSP (Digital Signal Processor) and anencoding and a decoding module. The processing unit 906 can be a singleunit or a plurality of units to perform different actions of proceduresdescribed herein. The arrangement 900 also comprises the input unit 902for receiving signals, such as information on the lines in a vectoringgroup, and the output unit 904 for output signal/s, such as, e.g.precoder update information. The input unit 902 and the output unit 904may be arranged as one.

Furthermore the arrangement 900 comprises at least one computer programproduct 908 in the form of a non-volatile memory, e.g. an EEPROM(Electrically Erasable Programmable Read-Only Memory), a flash memoryand a disk drive. The computer program product 908 comprises a computerprogram 910, which comprises code means, which when run in theprocessing unit 906 in the arrangement 900 causes the arrangement and/orthe VCE to perform the actions of the procedures described earlier inconjunction with FIG. 1.

Hence in the exemplary embodiments described, the code means in thecomputer program 910 of the arrangement 900 comprises a determiningmodule 910 a, determining if there are partial-vectoring resources to beallocated, and whether certain other criteria are fulfilled. Thecomputer program further comprises a calculating module 910 b forcalculating RBM-values. The computer program further comprises anallocating module 910 c allocating vectoring resources to the lines,based on the calculated RBM-values.

The computer program 910 is in the form of computer program codestructured in computer program modules. The modules 910 a-c couldessentially perform the actions of the flows illustrated in FIG. 1, toemulate the arrangement in a VCE illustrated in FIG. 8. In other words,when the different modules 910 a-c are run on the processing unit 906,they correspond to the units 802-810 of FIG. 8.

Although the code means in the embodiment disclosed above in conjunctionwith FIG. 9 are implemented as computer program modules which when runon the processing unit causes the arrangement and/or VCE to perform theactions described above in the conjunction with figures mentioned above,at least one of the code means may in alternative embodiments beimplemented at least partly as hardware circuits.

The processor may not only be a single CPU (Central processing unit),but could comprise two or more processing units in the devices. Forexample, the processor may include general purpose microprocessors,instruction set processors and/or related chips sets and/or specialpurpose microprocessors such as ASICs (Application Specific IntegratedCircuit). The processor may also comprise board memory for cachingpurposes. The computer program may be carried by a computer programproduct connected to the processor. The computer program productcomprises a computer readable medium on which the computer program isstored. For example, the computer program product may be a flash memory,a RAM (Random-access memory) ROM (Read-Only Memory) or an EEPROM(Electrically Erasable Programmable ROM), and the computer programmodules described above could in alternative embodiments be distributedon different computer program products in the form of memories withinthe VCE.

Some Remarks

The invention is completely compliant with the ITU-T G.993.5 [1]standard. It can transparently support partial vectoring with itsconfiguration parameters, i.e. target data/bit rate and line priority.

While the process as suggested above has been described with referenceto specific embodiments provided as examples, the description isgenerally only intended to illustrate the inventive concept and shouldnot be taken as limiting the scope of the suggested methods andarrangements, which are defined by the appended claims.

It is also to be understood that the choice of interacting units, aswell as the naming of the units are only for exemplifying purpose, andVCEs suitable to execute any of the methods described above may beconfigured in a plurality of alternative ways in order to be able toexecute the suggested process actions.

It should also be noted that the units described in this disclosure areto be regarded as logical entities and not with necessity as separatephysical entities.

ABBREVIATIONS

-   CEI Crosstalk Effect Indicator (defined within this disclosure)-   CPE Customer Premises Equipment-   DSL Digital Subscriber Line-   DSLAM Digital Subscriber Line Access Multiplexer-   FEXT Far-end crosstalk-   ODN Out-of-domain noise-   RBM Rate balancing metric-   SNR Signal-to-noise ratio-   SXL Sorted crosstalker list-   VCE Vectoring Control Entity-   VDSL2 Very high speed digital subscriber line transceivers 2

REFERENCES

-   [1] Draft Recommendation ITU-T G.993.5 Self-FEXT Cancellation    (Vectoring) for use with VDSL2 transceivers-   [2] Recommendation ITU-T G.993.2 Very High Speed Digital Subscriber    Line Transceivers 2 (VDSL2)

The invention claimed is:
 1. A method in a Vector Control Entity associated with a plurality of digital subscriber lines forming a vectoring group comprising a group A of lines having the same priority, the method comprising: when partial-vectoring resources are to be allocated among the lines within the vectoring group: calculating a rate balancing metric, RBM, for each line i within the group A, indicative of a ratio between a bit rate of line i with a current vectoring resource allocation, and an estimated bit rate of line i assuming approximately no crosstalk within the vectoring group, calculating an updated RBM for any line within the group A subjected to changes in vectoring resource allocation, and allocating partial-vectoring resources to the line/s within the group A, based on the calculated RBMs, such as to reduce the difference in RBM between the lines, thus enabling a fair bit rate distribution among lines of similar priority when applying partial vectoring.
 2. The method according to claim 1, wherein the allocation of partial-vectoring resources and a following update of RBM are repeated until one or more of the following apply: a lowest RBM is equal to or larger than a predetermined threshold, there are not vectoring resources sufficient for cancelling the crosstalk from another line within the vectoring group to a line within the group A, left to allocate, and there are not vectoring resources sufficient for cancelling any crosstalk left to allocate.
 3. The method according to claim 1, wherein any line within group A, of which the bit rate would exceed a predetermined maximal bit rate after a further allocation of vectoring resources is excluded from such allocation.
 4. The method according to claim 1, wherein any line within group A, for which the crosstalk from the other lines within the vectoring group is approximately cancelled, is excluded from further allocation of vectoring resources.
 5. The method according to claim 1, wherein partial-vectoring resources are allocated to a line having a low RBM, as compared to the other lines within group A.
 6. The method according to claim 1, wherein partial-vectoring resources are allocated to the line having the lowest RBM within the group A.
 7. The method according to claim 1, wherein partial-vectoring resources are re-allocated from one or more lines having a high RBM, as compared to the other lines within a group of lines having the same priority, when there are insufficient available vectoring resources left to allocate to a line which is to be joined to the vectoring group, or to a line which is to be upgraded to a higher priority.
 8. The method according to claim 7, wherein the partial-vectoring resources are re-allocated from the one or more lines having the highest RBM, as compared to the other lines within a group of lines having the same priority.
 9. An arrangement in a Vector Control Entity associated with a plurality of digital subscriber lines forming a vectoring group comprising a group A of lines having the same priority, the arrangement comprising: a calculating unit, adapted to calculate a rate balancing metric, RBM, for each line i within the group A, indicative of a ratio between a bit rate of line i with current vectoring resource allocation, and an estimated bit rate of line i assuming approximately no crosstalk within the vectoring group, and further adapted to calculate an updated RBM for any line within the group A subjected to changes in vectoring resource allocation, and an allocating unit, adapted to allocate vectoring resources to the line/s within the group A, based on the calculated RBMs, such as to reduce the differences in RBM between the lines, when partial-vectoring resources are to be allocated among the lines within the vectoring group, thus being adapted to enable a fair rate distribution among lines of similar priority when applying partial vectoring.
 10. The arrangement according to claim 9, further adapted to repeat the allocation of partial-vectoring resources and a following update of RBM until one or more of the following apply: a lowest RBM is equal to or larger than a predetermined threshold, there are not vectoring resources sufficient for cancelling the crosstalk from another line within the vectoring group to a line within the group A, left to allocate, and there are not vectoring resources sufficient for cancelling any crosstalk left to allocate.
 11. The arrangement according to claim 9, further adapted to exclude any line within group A, of which the bit rate would exceed a predetermined maximal bit rate after a further allocation of vectoring resources, from such allocation.
 12. The arrangement according to claim 9, further adapted to exclude any line within group A, for which the crosstalk from the other lines within the vectoring group is approximately cancelled, from further allocation of vectoring resources.
 13. The arrangement according to claim 9, further adapted to allocate partial-vectoring resources to a line having a low RBM, as compared to the other lines within group A.
 14. The arrangement according to claim 9, further adapted to allocate partial-vectoring resources to the line having the lowest RBM within the group A.
 15. The arrangement according to claim 9, further adapted to re-allocate partial-vectoring resources from one or more lines having a high RBM, as compared to the other lines within a group of lines having the same priority, when there are insufficient available vectoring resources left to allocate to a line which is to be joined to the vectoring group, or to a line which is to be upgraded to a higher priority.
 16. The arrangement according to claim 15, further adapted to re-allocate the partial-vectoring resources from the one or more lines having the highest RBM, as compared to the other lines within a group of lines having the same priority.
 17. A non-transitory computer-readable storage medium, comprising computer readable code means, which when run in one or more processing units, causes a Vector Control Entity associated with a plurality of digital subscriber lines forming a vectoring group comprising a group A of lines having the same priority, to perform a method comprising: when partial-vectoring resources are to be allocated among the lines within the vectoring group: calculating a rate balancing metric, RBM, for each line i within the group A, indicative of a ratio between a bit rate of line i with a current vectoring resource allocation, and an estimated bit rate of line i assuming approximately no crosstalk within the vectoring group, calculating an updated RBM for any line within the group A subjected to changes in vectoring resource allocation and allocating partial-vectoring resources to the line/s within the group A, based on the calculated RBMs such as to reduce the difference in RBM between the lines, thus enabling a fair bit rate distribution among lines of similar priority when applying partial vectoring. 